Glass scoring is one of the fundamental processes in the manufacture of sheet glass. It is used to form a “vent” in the glass surface which extends partially, but not completely, through the thickness of the glass. Once formed, the vent functions as a separation line for controlled separation of the glass into two pieces by applying a bending moment or other mechanical force to the glass at the vent.
Mechanical scoring is used at various points in the glass manufacturing process. For example, it is used during the initial separation of individual glass sheets from a moving glass ribbon. It is also used during trimming of individual glass sheets to desired dimensions, as well as in the division of large glass sheets into smaller sub-pieces.
FIG. 1 shows the basic components of an automated mechanical scoring system. In this figure, 100 is a glass sheet (e.g., a moving glass ribbon), 20 is a scoring assembly having a scoring head 21, and 30 is a platen assembly which includes a platen 31. During scoring, the scoring head (e.g., a scoring wheel or a scoring point) is moved across a major surface of the glass sheet (referred to herein as the “front surface”) along a predetermined path to form the desired vent. To support the glass during this process, the platen (i.e., a compliant platen in the prior art) is brought into contact with the opposite surface of the glass sheet (referred to herein as the “rear surface”). Examples of such platens (also known as “nosings”) can be found in commonly-assigned U.S. Patent Application Publications Nos. US2008/0276646 and US 2009/250497A1, the contents of which in their entireties are incorporated herein by reference.
In the past, the use of a compliant platen to support the rear surface of a glass sheet during mechanical scoring has worked successfully with glass sheets having thicknesses above 500 microns, e.g., glass sheets having a thickness of 700 microns as used as substrates in the manufacture of liquid crystal displays. However, as detailed below, in accordance with the present disclosure, it has been found that the compliant platens used with thick glass do not work successfully with thin glass, i.e., glass having a thickness that is less than or equal to 500 microns. In particular, it has been found that the combination of a thin glass sheet and a compliant platen (i.e., a platen having a compliant glass-engaging surface) leads to unreliable scoring. In accordance with one of its aspects, the present disclosure addresses this problem.
In addition to the problem with compliant platens, it has also been found that when mechanical scoring is used repetitively with thin glass, e.g., in connection with the separation of individual glass sheets from a glass ribbon, rather than producing a vent as desired, the process results in cracking of the glass at the location of the score head in an uncontrolled manner. Moreover, the percentage of cracked sheets grows as the process is continued, i.e., the process enters into a “death spiral.”
In accordance with another aspect, the present disclosure addresses this problem of uncontrolled cracking during the mechanical scoring of thin glass sheets. It both identifies the source of the problem and provides effective solutions to the problem that can be readily implemented in, for example, the context of an existing mechanical scoring process.